1. Field of the Invention
The present invention relates to a robot control device and, more particularly, to a robot control device capable of switching between a first operation mode for preventing an operator from approaching a robot working area when power is supplied to a drive motor for driving the robot and a second operation mode for allowing an operator to approach the robot working area even when power is supplied to the drive motor.
2. Description of the Related Art
A robot is generally operated automatically. Therefore, if an operator carelessly intrudes into a robot working area, the operator may collide with the robot. Thus, it is common practice to provide a guard fence or a light curtain around the robot and surround the robot working area with the guard fence or the light curtain to limit the robot working area to within the guard fence or the light curtain. As long as the operator stays outside the guard fence or the light curtain, there is no risk of the operator contacting the robot and the operator's safety is thus insured. Further, in the case where the operator intrudes into the robot working area through the door of the guard fence or the light curtain while the robot is in operation, the robot operation is forcibly stopped to secure the operator's safety.
For example, in the case where a guard fence is used, when a robot control device senses, based on the output from a door switch or a safety plug mounted on the door of the guard fence, that the door of the guard fence is opened, it determines that the operator has entered the area within the guard fence and immediately brings the robot to an emergency stop by cutting off the power supply to the robot. In the case where a light curtain is used, the robot control device senses that light of the light curtain has been intercepted, determines that the operator has entered the area within the robot working area and immediately stops the robot by cutting off the power supplied to the robot.
However, when teaching the robot about an operation, the operator is required to enter the robot working area through the door of the guard fence or the light curtain and perform the teaching job by operating the powered robot through a teaching pendant. Therefore, in addition to an automatic operation mode for sensing the intrusion of the operator into the robot working area and bringing the robot to an emergency stop, it is common practice to provide the robot control device with a teaching operation mode for allowing the robot to be operated without an emergency stop even if the operator enters the robot working area. In the teaching operation mode, the operator can operate an operation mode change-over switch on a fixed operation panel of the robot control device to switch between the automatic operation mode and the teaching operation mode.
In the teaching operation mode, the signal from the door of the guard fence or the light curtain is invalidated even when the door of the guard fence is opened or the operator intrudes into the robot working area through the light curtain, so that the operator can operate the robot from the teaching pendant without stopping the robot as an emergency. In addition, in order to secure the safety of the operator even in the teaching operation mode, as described in Japanese Unexamined Patent Publication No. 8-166814, an emergency stop button and a deadman switch are provided on the teaching pendant, so that the robot can be operated only while depressing the deadman switch. The operator, whenever danger is perceived, can release the deadman switch, or depress the emergency stop button on the teaching pendant, to thereby bring the robot to an emergency stop even in the teaching operation mode.
As described above, the robot can be brought to an emergency by operating the emergency stop button or the deadman switch even in the teaching operation mode. However, in order to positively guarantee sufficient safety of the operator, it is necessary to confirm, before starting the teaching job, that an emergency stop circuit functions normally upon depression of the emergency stop button or operation of the deadman switch. In the prior art, the emergency stop circuit is checked manually by the operator, and therefore the check job is sometimes forgotten or intentionally omitted. As a result, the safety of the operator cannot be secured in some cases where the emergency stop circuit fails and an emergency stop cannot be carried out.